The shipment of temperature-sensitive goods is extremely difficult when the shipping container itself is not independently temperature-controlled; ie, does not have an independent power source for maintaining interior temperatures within close parameters. Of course, if it is merely desired to maintain an object to be shipped at a nominally cooled temperature—relative to the ambient exterior temperature—a common practice is to pack a shipping container with ice, and hope that the ice will remain in a frozen state during transit so that the object shipped will arrive at its destination still cooled below ambient temperature. This can be an adequate technique for shipping objects where temperature control is not critical. However, even in this case, the temperatures at different points inside the shipping container will vary widely, with parts of the interior of the container becoming quite cool and other parts of the interior warming to various degrees, depending on time and the distance and spatial relationship of the shipped object to the cooling ice which remains in the container.
In shipping objects for which the ambient temperature is expected to be cooler than the desired temperature for the object, the common practice is to place the warmed object inside a container having insulated walls, and then to hope the shipping time is shorter than the time for the heat inside the container to escape through the insulated walls.
A need exists for a passive, reliable and relatively inexpensive way to protect highly temperature-sensitive products and materials. Such products and materials are usually fairly high in value and may be extremely temperature-sensitive. Some examples of such products or materials are blood shipped or carried to remote battle zones, sensitive pharmaceuticals shipped between plants or to distributors, HIV vaccines shipped to third world countries, and medical instruments shipped to, or kept in readiness at, remote stations or in emergency vehicles. In such cases the ambient temperatures may vary widely, from extremely hot shipping facilities in the southern states to receiving points in cold, mountainous regions of the world in midwinter.
In the prior art temperature control of shipped products or materials has been at least partially achieved by using containers lined with insulating panels on all six outer wall surfaces, and then including in the container with the product or material a pack or package of material which acts as either a heat sink (ie., ice) or heat source (ie., water), depending on whether the container is expected to encounter higher or lower ambient temperatures during shipment. The required wall thickness of the insulated container walls, and the volume of heat sink, or heat source, material can be approximately empirically determined by testing, to identify an expected average interior temperature dependent on choice of materials, wall thickness, expected ambient temperatures during shipment, and time of shipment. However, this testing cannot reliably identify the range of internal temperatures which might be encountered, which depend upon the spatial relationship between the internal shipped object and the various other factors described above.